Inhibition of escape tailflip in crayfish during backward walking and the defense posture.

A major question in neuroethology is how animals coordinate transitions between incompatible behavior patterns. The recent demonstration that the lateral giant (LG) tailflip is inhibited during eating (Krasne and Lee, 1988) suggested to us that inhibition may play a general role in preventing maladaptive transitions between incompatible behavior patterns. We wished to determine whether the LG tailflip is inhibited during other incompatible behavior such as backward walking and the defense posture. Different behavior patterns are incompatible because they move the same body parts differently and because they are adaptive responses to different sensory stimuli. This is the case with backward walking, defense posture and escape tailflip in crayfish. Backward walking is frequently observed among crayfish living communally in a laboratory aquarium, often in response to stimuli that signal potential rather than immediate danger, or in response to possible conflict with conspecifics. These stimuli include tactile stimulation of the antennae, approach of threatening visual stimuli, illumination of the eyes and/or illumination of the caudal photoreceptors in the last abdominal ganglion (Welsh, 1934; Kovac, 1974; Edwards, 1984; Simon and Edwards, 1990). The defense posture is a threat display that occurs in response to looming visual stimuli and consists of raising and spreading the chelipeds towards the stimulus, raising the cephalothorax by extending the legs in a widened stance, and extending and flattening the abdomen against the substratum. Escape tailflip occurs in response to immediately threatening stimuli, to direct attacks or blows, or during conflict with conspecifics (Wine and Krasne, 1972, 1982). The upwardly directed, somersault tailflip can be triggered by a sharp tap on the dorsal abdominal surface; the tap excites mechanosensory afferents and mechanosensory interneurons that converge on the bilaterally paired LG interneurons. These cells act as 'decision neurons' for the behavior (Zucker, 1972; Olson and Krasne, 1981).